RESUMO
PURPOSE: The development of fibrous nonunions after orthognathic surgery is thought to result from an interaction of biomechanical stress and the differential and more rapid migration of fibroblasts (compared with osteoblasts) into the wound site during healing. The present study was designed to test this hypothesis through the manipulation of guided tissue regeneration and osteotomy fixation techniques in an experimental rabbit model. MATERIALS AND METHODS: Bilateral critical size (4 mm) defects (n = 24) were produced in the maxillae of 12 adult New Zealand white rabbits. The maxillary segments were rigidly or nonrigidly fixed using bone microplates and screws or osteosynthetic wires. The defects were then covered with a resorbable collagen membrane or left uncovered. The rabbits were followed for 4 weeks with the use of serial dorsoventral and lateral oblique cephalographs, and the maxillae were then harvested for histologic analyses. RESULTS: Radiographic and histomorphometric analyses revealed that rigidly fixed defects, covered with membrane, showed the most rapid and organized new bone formation. The rigidly fixed defects with the membrane averaged approximately 40% more new bone in the osteotomy site compared with the rigidly fixed defects with no membrane. Nonrigidly fixed defects with no membrane showed an ingrowth of fibroblasts and fibrous nonunions. CONCLUSIONS: These experimental results suggest that an interaction between the decreased fibrous tissue ingrowth through guided tissue regeneration and osteotomy segment stability from rigid fixation prevented postoperative fibrous nonunions and facilitated new bone regeneration and osteotomy site healing in this rabbit model.
